The present invention relates to a disc drive apparatus in which a vibration damper is integrated. The vibration damper arrests self-vibration of a disc due to unbalance of the disc per se. The disc is a medium used in a CD-ROM drive apparatus or a CD-R drive apparatus. This vibration damper allows the disc drive apparatus to record/reproduce data in a stable manner.
A data transfer rate of a disc drive apparatusxe2x80x94recording/reproducing dataxe2x80x94employed in a CD-ROM or CD-R drive apparatus has recently become higher and higher. This requires a disc to revolve at a higher speed.
In general, many discs have uneven thickness, which causes unbalance in mass of the disc. When such a disc is driven at a high speed, the following inconveniences are produced: Self-vibration is produced by unbalance force of the disc, and the vibration travels to overall apparatus, so that data cannot be reproduced in a stable manner, and the vibration yields noise as well as shortens the service life of the motor. When the disc drive apparatus is integrated into a computer system, the vibration may travel to other peripherals and adversely affect them.
At a higher data-transfer-rate by spinning the disc at a higher speed, i.e. revolutions per minute (rpm), the self-vibration due to disc""s unbalance is desirably arrested. For that purpose, various measures have been proposed to cancel the unbalance of the disc. The Japanese Patent Application Non-Examined Publication No. H10-83622 proposes one of the measures.
A disc drive apparatus having a conventional canceling function is described hereinafter.
FIG. 5 is a perspective view of a conventional optical disc drive apparatus having a balancer to cancel the unbalance of centrifugal force at revolving the disc. FIG. 6 is a lateral cross section of the essential part of the same apparatus. FIG. 7 is a cross section viewed from the top illustrating the balancer.
In FIG. 5, on main base 8 of the optical disc drive apparatus, the following elements are arranged to function as described below:
Spindle motor 2 spins disc 1. Photo pickup 3 reads data recorded in disc 1 or write data into disc 1. Photo pickup driving system 5 comprises a rack and a pinion. Driving system 5 transduces rotational motion of motor 4 into linear motion of pickup 3. Motor 4 is used for driving the photo pickup. At this time, driving system 5 moves pickup 3 in radial direction of disc 1. Spindle motor 2, motor 4 and driving system 5 are mounted on sub-base 6.
Elastic isolator 7 damps vibrations and shocks coming from the outside of the apparatus and travelling to sub-base 6. Sub-base 6 is mounted to main base 8 with isolator 7 in between. At a high rpm of disc 1, isolator 7 is deformed, which produces a resonant frequency of sub-base 6. The resonant frequency is set at a lower level than a rotating frequency of disc 1 driven at a high rpm, so that the vibrations or shocks from the outside is damped by isolator 7.
In FIG. 6, ferromagnetic yoke 11 is fixed to turntable 9, and turntable 9 spins unitarily with spindle motor 2. Clamp 10 incorporates magnet 271. Disc 1 is held by turntable 9 and clamp 10 due to magnet attraction between magnet 271 and yoke 11, and is unitarily spun with turntable 9.
Polarized face 28 of magnet 271 is usually polarized two polarities (N and S poles in pair), as shown in FIG. 7, for easy manufacturing as well as due to a simple application. On the other hand, back-yoke 15 made of ferromagnetic substance is disposed on non-polarized face 29 of magnet 271. Back-yoke 15 shuts out leakage magnetic flux from others except polarized face 28, so that magnetic flux travelling from face 28 to yoke 11 is efficiently secured. This strengthens attraction between magnet 271 and yoke 11. As a result, disc 1 is held more firmly between clamp 10 and turntable 9.
Hollow annular section 14 of clamp 10 accommodates a plurality of movable balls 13 (single ball position 131, 132, and onward) made of magnetic substance. Ball position 131 indicates its location at a high rpm, and centrifugal force urges ball position 131 against outer wall 20 of hollow annular section 14. In this condition, ball 13 at position 131 revolves. Ball position 132, on the other hand, indicates its location at a low rpm. In this case, ball 13 at position 132 is attracted to the inner wall of hollow annular section 14, i.e. the outer wall of magnet 271, by attraction of magnet 271. The balancer comprises clamp 10, balls 13, magnet 271 and back yoke 15. This balancer is mounted on sub-base 6 via disc 1, turntable 9 and spindle motor 2. Sub-base 6 is coupled to main base 8 via isolator 7. As already discussed, high speed rotation of disc 1 deforms isolator 7, and the resonant frequency of sub-base 6 due to the deformation of isolator 7 is set at a lower level than the rotating frequency of disc 1 revolving at a high rpm.
FIG. 7 is a cross section of clamp 10 viewed from the top. FIG. 7 illustrates how the unbalance is cancelled at a high rpm of disc 1 by the movement of balls 13 housed in clamp 10.
A status of balls 13 at a low rpm of unbalance disc 1 is described, and how the unbalance of disc 1 is cancelled at a high rpm is also described hereinafter.
In a CD-ROM drive apparatus, in general, the disc is spun at a higher speed (in eight times mode, max ca. 4200 rpm) in order to increase data transfer rate in the data read mode. On the other hand, the disc is spun at a standard rate (ca. 200-500 rpm) in an audio play mode. As such, a high rpm for data read and a low rpm for audio play are intermingled.
When disc 1 having unbalance is spun at a high rpm, unbalance force, namely centrifugal force, acts to gravity center 17 of disc 1, and the act-direction revolves together with disc 1. This unbalance force 18 deforms isolator 7, and sub-base 6 vibrates at a rotating frequency of disc 1. Since the resonant frequency of sub-base 6 is set at a lower level than the rotating frequency of disc 1, the displacement direction of sub-base 6 is always reverse to the direction of unbalance force 18. As a result, balls 13 housed movably in clamp 10 receive resultant force of centrifugal force 19 and resistant force 21 from wall 20 to which balls 13 are urged. This resultant force functions as moving force 22. Balls 13 thus move away from vibrating center 23 and collect in the right reverse direction to unbalance force 18. Finally, a total mass of balls 13 gathered at ball position 131 at the high rpm cancels unbalance volume of disc 1.
In a low rpm area including a standard rate, centrifugal force 19 of balls 13 decreases, which cannot keep urging balls 13 onto wall 20. Balls 13 then become unstable, so that various noises are generated such as rolling and sliding of balls 13 on the walls within clamp 10, and collision between balls 13.
In the low rpm area, if the unbalance force is negligible small and centrifugal force urges balls 13 against wall 20, the unbalance force would increase because the centrifugal force acts to balls 13.
For avoiding this problem, balls 13 are to be made of magnetic substance, and balls 13 are urged to outer wall 26 of magnet 271 and back yoke 15 by utilizing leakage magnetic flux 24 of magnet 271 or magnetic flux 25 travelling from polarized face 28 to back yoke 15. As a result, balls 13 are rested at ball position 132 at a low rpm, thereby preventing the noises from being generated.
However, in the conventional structure discussed above, there may be the following problem when disc 1 suddenly changes its rotating rate from a high rpm to a low rpm.
A disc to be loaded to a CD-ROM drive apparatus includes normal data intermingled with audio data. When such a disc is played back, the normal data are read at the high rpm and then the rpm is changed to the standard one to play back the audio data. In other words, there may be a case, where the disc is spun at the high rpm and suddenly the rotating speed is changed to the low rpm, then the audio data must be played back right after this change.
As discussed previously, balls 13 are urged to wall 20 of hollow annular section 14 and spun unitarily with clamp 10 so that the unbalance of disc 1 is cancelled at the high rpm. However, when the rotating speed lowers to a given speed, the centrifugal force applied to balls 13 decreases. Then balls 13 are attracted to outer wall 26 and yoke 15 due to leakage magnetic flux 24 of magnet 271 as well as magnetic flux 25 travelling from polarized face 28 to back yoke 15. Yet, polarized face 28 of magnet 271 is polarized two polarities, and in the case of the two polarities, leakage magnetic flux 24 becomes greater while the density of magnetic flux 25 becomes smaller. Because of this characteristics, balls 13 are difficult to be released from outer wall 26 of magnet 271 when disc 1 undergoes the change from a low rpm to a high rpm. On the contrary, when disc 1 undergoes the change from the high rpm to the low rpm, balls 13 are difficult to be attracted to outer wall 26 because balls 13 won""t be released from wall 20 unless centrifugal force 19 applied to balls 13 substantially decreases.
As such, in the case that normal data is read at a high rpm and then audio play starts just after the data-read, the characteristics of balls 13xe2x80x94difficult to be released from wall 20 and difficult to be attracted to wall 26xe2x80x94allow balls 13 to be attracted to wall 26 after the audio data starts being read. The shock by the attraction travels to disc 1, and may cause a read-error.
When a disc start spinning, namely at the spin-up, balls 13 won""t be released from wall 26 because of great leakage magnetic flux 24. When the rotating speed reaches to highly enough level, balls 13 are released from wall 26 and crash to wall 20, the shock becomes greater at the higher speed. As a result, this crash may cause defectives such as exceeding a spin-up time.
The present invention addresses the problems discussed above and aims to cancel unbalance efficiently by utilizing the centrifugal force of balls at a high rpm where the unbalance of a disc reveals as a problem. The present invention also aims to prevent noises from being generated by resting the balls at a low rpm including an audio-play mode. Further, the present invention provides a disc drive apparatus free from read-errors even when the disc undergoes a sudden change from the high rpm to the low rpm or at a spin-up.
The disc drive apparatus of the present invention comprises the following elements:
a balancer having a hollow annular section and being spun with a disc unitarily;
a magnetic substance housed in the hollow annular section;
a magnetic generator for generating magnetic flux which couples with the magnetic substance through electric-magnetic transducing; and
a controller for controlling an output from the magnetic generator.
This structure allows the controller to control, responsive to the need, the intensity of magnetic field which attracts and retains the magnetic substance, thereby controlling the balance of the disc more finely. As a result, shocks to the wall of the hollow annular section by the magnetic substance can be decreased, and in particular, read-errors at the change of disc rpm can be substantially reduced.
The controller can continue switching on/off the magnetic generator intermittently so that when the rpm is changed from low to high, and after the change and when the rpm becomes stable, the magnetic field for attracting and retaining the magnetic substance can be switched off. As a result, read-errors are reduced as well as the power consumption of the magnetic generator is lowered.